Thermal energy storage

ABSTRACT

A thermal storage (TES) unit includes an encasement with inner and outer surfaces. The TES unit includes an internal cavity surrounded by the inner surface of the encasement and at least a fin disposed in the cavity. The fin separates the cavity into a plurality of sub-cavities and includes openings to provide communication between the sub-cavities. A phase change material (PCM) is to be disposed within the encasement. The PCM includes a threshold temperature T T , a first temperature range corresponding to a first phase of the PCM and a second temperature range corresponding to a second phase of the PCM. The fin increases thermal transfer efficiency of the thermal energy between external environment of the TES unit and PCM. The TES unit can be incorporated for heating and cooling applications.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Indian Patent Application No. 2118/CHE/2008, filed on Aug. 29, 2008 in India (IN), the entire contents of which are herein incorporated by reference.

BACKGROUND

Demand to store or sustain thermal energy to be supplied continuously at all time in desired temperatures for various domestic or industry purposes have increased tremendously in recent years. The storing or sustaining of thermal energy through conventional energy sources such as electricity and pumps to sustain thermal energy in various desired temperatures and for prolonged period requires high costs to build utilities, operation, and maintenance of power plants and size of network distribution and appreciable electric load consumption in electrical arrangements.

In view of the high costs involved to provide thermal energy for different applications based on conventional resources, alternative energy sources, for example, solar energy has emerged as a promising candidate as it is inexpensive and renewable in nature. However, due to the limited day light for harnessing solar energy, a more cost and energy effective solution to harness thermal energy is required such that thermal energy can be supplied at all time and in various weather conditions as well.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

FIGS. 1 a-e show various embodiments of a thermal energy storage unit;

FIGS. 2 a-b show different embodiments of encasements for thermal energy storage units;

FIGS. 3 a-b-FIGS. 5 a-b show different embodiments of cross-sectional views of segments for thermal energy storage units;

FIG. 6 shows an embodiment of a thermal storage system;

FIG. 7 shows an embodiment of a thermal energy storage system; and

FIG. 8 shows an embodiment of a process for storing and sustaining thermal energy.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure. This disclosure is drawn, inter alia, to methods, apparatus and systems related to storing and sustaining thermal energy. The system may be used on its own as a standalone system or it may be used in multiplicity as part of a larger system.

FIG. 1 a shows a thermal energy storage (TES) unit 110. The TES unit stores thermal energy that can be dissipated to sustain a thermal transfer medium at a desired temperature until the thermal energy is exhausted. The thermal transfer medium comprises a working fluid, such as water. In alternative embodiments, other types of working fluids, such as low temperature boiling point fluids or high temperature boiling point fluids can be used. In yet other embodiments, other types of media, such as ethylene glycol or gas, can be employed.

The TES unit includes an encasement 115. The encasement includes a hollow interior for storing a thermal energy storage material, embodiments of which are described below. The encasement should be designed to produce efficient heat transfer. In one embodiment, the encasement has a spherical shape. Other geometrical shapes can also be used in other embodiments. For example, the encasement may have a rectangular, a cylindrical, an oval or an elliptical shape, as shown in FIGS. 1 b-e. The encasement can be provided in different sizes or diameters. The shape or size of the encasement, for example, can depend on the application, such as the size of the storage tank containing the medium. In one embodiment, the encasement has a diameter D of about 1-12 inches. In other embodiments, the diameter of the encasement may be about 1-2 inches.

The encasement of the TES unit can be made of a thermal conductive material. Various types of thermal conductive materials may be used to form the encasement. For example, the thermal conductive material can be stainless steel, copper, tin, aluminum, alloys thereof or a combination thereof. In alternative embodiments, other types of materials can be used.

The thermal energy storage material, in one embodiment, includes a phase change material (PCM), embodiments of which are described below in conjunction with FIG. 7. The PCM has a threshold temperature T_(T). At a temperature range from T₁ to T_(T) (first temperature range or T_(R1)), the PCM has a first phase while from T_(T) to T₂ (second temperature range T_(R2)), the PCM has a second phase. In one embodiment, T_(T) is the melting temperature of the PCM.

During charging, the thermal energy from the encasement transfers to the PCM for storage. For purposes of discussion, the PCM has a first phase during charging. For example, the temperature of the PCM is within T_(R1) prior to charging. The charging temperature of the PCM has a temperature in the second temperature range. The magnitude of T_(R), for example, can depend on the application or desired charging rate.

As the temperature of the PCM migrates to T_(R2), the PCM begins to transform from the first phase to the second phase. Energy continues to be stored until the PCM reaches full storage capacity when it is completely in the second phase. The thermal energy stored in the PCM at full capacity can be referred to as latent thermal energy. Energy stored beyond full capacity can be referred to as sensible thermal energy.

For heating applications, the T_(T) of the PCM can be selected to be about 58° C.-65° C. The T_(T) of the PCM can have other temperatures in other embodiments. In one embodiment, the first phase has a solid phase while the second phase has a liquid phase. During charging the PCM is heated above T_(T). This causes the PCM to change to the liquid phase as it stores latent thermal energy. The latent thermal energy storage reaches full capacity when the PCM is completely in the liquid phase. When the PCM is cooled, it begins to solidify which results in the PCM releasing latent thermal energy (discharging) to sustain the temperature at about T_(T).

For cooling applications, the T_(T) of the PCM can be selected to be about 20° C.-30° C. In other embodiments, the T_(T) of the PCM can have other temperatures. In one embodiment, the first phase has a liquid phase while the second phase has a solid phase. During charging the PCM is cooled below T_(T). This causes the PCM to change from the liquid phase to the solid phase as it stores latent thermal energy. The latent thermal energy storage reaches full capacity when the PCM is completely in the solid phase. When the PCM is heated, it begins to liquify which results in the PCM releasing latent thermal energy (discharging) to sustain the temperature at about T_(T).

FIGS. 2 a-b show different encasements for a TES unit 110. Referring to FIG. 2 a, the encasement 115 includes first and second segments 220 a-b. As shown, the segments represent first and second halves of a spherical shaped encasement. Fins 240 a-b, in one embodiment, are disposed in the interior portions 225 a-b. In one embodiment, the fins include elongated members. The fins, for example, include flat elongated members. Other types of fins can also be used in other embodiments. The fins may be formed from various types of materials. For example, the fins can be formed from thermal conductive materials such as stainless steel, mild steel, copper, tin, aluminum, alloys thereof or a combination thereof. The fins and the encasement can be made from the same or different materials. The fins and the encasement can be formed from separate pieces of material and coupled by, for example welding, brazing or soldering. In other embodiments, the encasement and fins can be formed from the same piece of material, such as by casting. In yet other embodiments, the fins can be formed using different techniques or different materials.

The fins divide the interior portions of the segments into a plurality of sections in some embodiments. As shown, the fins separate the interior portions of the segments into first and second sections 228 ₁₋₂. In other embodiments, the interior portions can be separated into other number of sections or sub-portions. For example, as shown in FIG. 2 b, the fins divide the interior portions into first, second, third and fourth sections 228 ₁₋₄. In one embodiment, the sections have about the same volume. The sections, in other embodiments, can be of different volumes or a combination of same and different volumes.

In one embodiment, the fins are in thermal communication with the encasements while partially separating the interior portions into sections. By partially separating the interior portions, the sections are in communication with each other. In one embodiment, the segments are partially separated by providing fins which are partially coupled to the interior surfaces of the segments.

FIGS. 3 a-b show cross-sectional views of segments of different embodiments of encasements. FIG. 3 a corresponds to fins of a segment of FIG. 2 a while FIG. 3 b corresponds to fins of a segment of FIG. 2 b. As shown, the fins are partially coupled to an inner surface of the interior portion at the bottom portion of the segment, leaving spaces 242 which separate the fins from sides of the interior surface.

The fins, in other embodiments, can be coupled to different parts of the interior surfaces of the segments to provide partial separation between the sections, as shown in FIGS. 4 a-b. FIG. 4 a may correspond to fins of a segment of FIG. 2 a while FIG. 4 b may correspond to fins of a segment of FIG. 2 b. As illustrated, the fins are partially coupled to an inner surface of the interior portion at the side portions of the segment, leaving spaces 242 which separate the fins from sides of the interior surface.

FIGS. 5 a-b show cross-sectional views of other embodiments of segments. FIG. 5 a corresponds to fins of a segment of FIG. 2 a while FIG. 5 b corresponds to fins of a segment of FIG. 2 b. As shown, the fins are coupled to the inner surface of the interior portion of the segment. The fins are provided with at least one slot or perforation 248 to enable communication between the sections. In one embodiment, the fins are provided with a plurality of slots or perforations in the fins. In yet other embodiments, the fins can be partially coupled to the interior surfaces of the segments and include slots or perforations. The ratio of slot area to fin area can be selected to meet design requirements. For example, the ratio of slot area to fin area can be selected for efficient thermal energy transfer between the environment and the TES unit.

The two segments can be coupled together. In one embodiment, the two segments can be coupled by welding. In one embodiment, the fins of the two segments can be aligned when coupled. Alternatively, the fins of the two segments can be misaligned. For example, in the case where the fins separate the interior portion into two sections, such as shown in FIG. 2 a, the fins can be arranged perpendicular to each other. Providing fins which are in thermal communication and partially separated sections improves PCM flow and thermal transfer efficiency, as well as prolonging the sustainability of thermal energy.

In one embodiment, one of the segments is provided with an opening (not shown) to facilitate filling of the TES unit with PCM. The PCM fills about 70%-80% of the volume of the encasement. In other embodiments, the PCM fills other percentage of volume of the encasement. The opening can be closed with a cap. In one embodiment, the cap includes a screw cap. An o-ring can be provided to hermetically seal the PCM in the encasement.

In other embodiments, the two segments can be coupled by screwing them together. For example, one segment can be provided with male threads while the other with female threads. An o-ring can be provided for hermetically sealing the encasement to prevent leakage of the PCM. In other embodiments, the two segments can be coupled using different coupling techniques. For example, the segments can be welded or soldered together. In such applications, the PCM can be disposed on the segments prior to being coupled. The PCM, for example, is disposed in the segments while in the solid phase.

FIG. 6 shows an embodiment of a thermal storage system 300. As shown, the system includes a tank or container 360 with an input port 362 and an output port 364. Although one input port and one output port are shown, it is understood that additional ports can be provided. The additional ports can serve different purposes. For example, additional input ports can be provided for increasing flow of the medium or for filling the tank to increase the volume of the medium. In one embodiment, the input port can be located lower than the output port. In one embodiment, the input port is located at or about the bottom of the tank while the output port is located at an upper portion of the tank. Alternatively, the ports can be located at other locations, depending on, for example, the application.

The tank can be made from various types of materials, such as glass or metal. The material selected may depend on, for example, the application. In one embodiment, the tank is formed from stainless steel or mild steel. To increase thermal efficiency, the tank may be insulated to retain thermal energy. Insulation materials, such as glass wool, can be used to insulate the tank. In alternative embodiments, other types of insulation materials or insulating designs can be used. The tank, as shown, has a rectangular shape or prism. In other embodiments, the tank can have different types of shape. For example, the tank can have a cylindrical shape. The size or volume of the tank can be designed to meet capacity requirements.

At least one TES unit 310 is disposed in the tank. In one embodiment, a plurality of TES units 310 are disposed in the tank. The TES units can be arranged in different configurations. In one embodiment, the TES units are freely disposed in the tank. The TES units, in other embodiments, can have different configurations. For example, the TES units can be arranged in a matrix or an array.

In one embodiment, a thermal transfer medium 308 circulates through the system. The medium circulates through the tank via the input and output ports. The medium can include, for example, water or other types of fluids. In alternative embodiments, the medium can include other types of media, such as low temperature boiling point fluids, high temperature boiling point fluids, ethylene glycol or gas. The medium employed depends on, for example, the application.

The medium contains thermal energy which is transferred to the TES units, charging them. The thermal energy, for example, can be imparted to the medium by an energy source. Various types of energy source can be employed. In one embodiment, the energy source derives or is powered by renewable energy, such as solar energy. In other embodiments, the energy source can be powered by a by-product of a primary process. The primary process can be powered by renewable energy, non-renewable energy or a combination thereof.

Circulating the medium in the system can be by various techniques. Such techniques can include an active process, a passive process or a combination thereof (hybrid process). For example, the active process can include a pump for circulating the medium, the passive process can include siphoning or convection effect due to temperature differential while a hybrid process includes a combination of pump and siphoning and/or convection effect. The medium can also be circulated, in alternative embodiments, using other types of techniques. The flow rate of the medium can be selected to meet design requirements.

The energy stored in the TES units can be used to sustain the medium at a desired temperature when the energy source is terminated. For example, when the energy source is switched off or unavailable. Sustaining the medium at the desired temperature is achieved by discharging or releasing the latent thermal energy stored in PCM of the TES units.

The TES units to tank ratio should be sufficient to sustain the medium at the desired temperature for a desired period of time after the energy source has become unavailable or terminated. In one embodiment, the TES units to tank ratio by volume is about 75%. In alternative embodiments, different TES units to tank ratio can be used, such as 60%-80%. The TES units to tank ratio may depend on the application, such as volume of medium and desired period of time.

FIG. 7 shows an embodiment of a thermal energy storage system 400. As shown, the thermal energy storage system includes a tank 460 and an energy source 470. The tank includes an input port 462, output port 464, fill port 466 and dispense port 468. The tank can be filled with a thermal transfer medium via, for example, the fill port located at about the top portion of the tank. In one embodiment, the thermal transfer medium includes water. In alternative embodiments, the medium can include other types of media. The medium can depend on the application.

The tank may include a cylindrical shape. In alternative embodiments, the tank includes other types of shapes. The tank can be made from stainless steel, mild steel, or aluminum. In alternative embodiments, other types of materials may be used for the tank. The tank may be insulated. Insulation materials, such as glass wool or other types of insulation materials, can be used to insulate the tank. In one embodiment, the size of the tank is about 100 liters. Alternatively, the tank can have other sizes. For example, the size of the tank can be selected to be appropriate to meet requirements, such as capacity, for a specific application.

At least one TES unit is disposed in the tank. In one embodiment, a plurality of TES units are disposed in the tank. The TES units may be freely placed into the tank. In other embodiments, the TES units can be arranged in different configurations. The tank, in one embodiment, includes sufficient amount of TES units. For example, the tank to TES units ratio may be about 75%. Different tank to TES units ratio can also be used for other embodiments.

The TES unit is filled with PCM. The PCM may include organic, inorganic materials or a combination thereof. For example, PCM that includes industrial wax having low melting temperature T_(T) in the range of about 58-65° C. can be used. PCM with other melting temperatures can be used for alternative embodiments.

In one embodiment, the energy source includes a renewable energy source. The renewable energy source includes a solar collector. The solar collector includes an input port 472 and an output port 474. The energy source is coupled to the tank. For example, the input port of the tank is coupled to the output port of the energy source while the output port of the tank is coupled to the input port of the energy source. To couple the tank and the energy source, fluid communication channels 478 are used. The fluid communication channels, for example, include rubber tubing. In other embodiments, different types of fluid communication channels can be used. The thermal transfer medium circulates between the tank and energy source via the communication channels. The size of the communication channels can be selected to satisfy design requirements, such as flow rate. In one embodiment, the size of the communication channels is about 1½ inch in diameter.

The tank, in one embodiment, is disposed above the energy source. For example, the tank is disposed about 1-2 feet above the energy source. In different embodiments, the tank may be disposed at other distances from the energy source. Valves can be disposed in the fluid communication channel to prevent reverse heat transfer. For example, the valves can be shut to prevent fluid flow between the tank and energy source when solar energy is unavailable.

The energy source imparts thermal energy to the thermal transfer medium. In one embodiment, the thermal energy includes a high temperature thermal energy to produce hot water. For example, the hot water can be about 58-65° C. The size of the solar collector should be sufficient to meet design requirements. For example, the solar collector is about 1×2 meters. In alternative embodiments, the solar collector can have other sizes. Additional solar collectors can also be used in other embodiments. In other embodiments, the energy source can include a combination of renewable and non-renewable energy sources.

Various types of solar collectors can be used. The solar collector, for example, includes a solar plate collector. The solar plate collector can include a simple glass topped insulated box with a flat solar absorber made of sheet metal attached to a conductor pipe 486. The conductor pipe can include copper or other types of efficient thermal transfer material. The pipe can optionally be painted in black, for example, to increase heat absorption. The solar collector can optionally include reflectors to focus the solar energy. In alternative embodiments, other types of solar collectors can be used. For example, spiral solar collectors can be employed. In yet other embodiments, the solar collector can be integrated as part of the tank. For example, the tank acts as both storage and solar collector.

The solar collector, in one embodiment, can be tilted using a stand 450. For example, the solar collection is tilted at about 70°. Tilting the solar collector at other angles may also be useful for other embodiments. The tilt angle can depend on, for example, geographical location. Also, the tilt angle can be dynamic, adjusting change in time.

In operation, the tank is filled with water. In one embodiment, since the tanks ports are located at the bottom of the tank, water flows into the solar collector. During the day, solar energy is collected by the solar collector. The solar energy heats the water flowing through the pipe of the solar collector. Due to the density difference of the heated water and the water in the tank, the water circulates through the system using siphoning principle. For example, cold water flows into the solar collector from the output port of the tank and heated water flows into the tank via its input port. This produces a passive or thermosiphon system which avoids the need of a pump to circulate the fluid. As such, no auxiliary energy is required to operate the pump, making the system more cost and energy efficient.

The heated water in the tank, when it contacts the TES units, charges them. As the temperature of the heated water in the tank exceeds T_(T), the PCM transforms from the solid phase to the liquid phase, which results in thermal energy being stored as latent thermal energy. When the PCM is completely melted, the PCM has reached it energy storage capacity.

As hot water in the tank is consumed, for example, through the dispense port, the tank can be refilled. The cold water is heated by the TES units as well as by the solar collector.

The TES units charge at different rates due to location in the tank. The fully charged TES units float on the water surface. Since the water at the top of the tank is relatively cooler than the heated water at the bottom, for example, due to refilling of the tank, the fully charged units discharges heat to heat the water at the surface. This causes the PCM to begin to solidify. As the PCM solidifies, the TES units start to sink. This results in the system transferring heat by convection and conduction. Additionally, the difference in temperature between the top and bottom of the tank causes water turbulence. The water turbulence rotates the TES units, causing the PCM therein to flow between the sections, making thermal energy transfer and storage more efficient.

When solar energy is unavailable, the water in the tank cools. The TES units discharge stored heat. The TES units dissipate stored sensible thermal energy to continue heating the water. As the sensible energy is exhausted, the water begins to cool below T_(T), which causes the PCM to solidify. As the PCM solidifies, it releases the stored latent thermal energy to sustain the water at about T_(T). By providing a sufficient amount of TES units, the water can be sustained at T_(T) until solar energy becomes available to recharge the TES units. Furthermore, by providing the tank above the energy source, reversal of heat exchange when solar energy is unavailable can be avoided.

The thermal energy storage system can also include a safety device 490 to ensure safety of the system during usage. The safety device, in one embodiment, includes a vent pipe. The vent pipe, in one embodiment, is located on a top surface of the tank. The vent pipe releases pressure which can build up in the tank. In other embodiments, other types of safety device, such as a pressure release valve, can be used.

The thermal storage system advantageously produces hot water cost effectively by using less or avoiding the need of non-renewable energy. The hot water can be used for human consumption. The hot water can also be used for other applications. For example, the hot water can be used for industrial as well as non-industrial purposes. Industrial purposes can include heating feed water for boilers, foundry core baking, cleaning or industrial heating or use in processing plants. In another embodiment, the thermal storage system can be adapted to fit around an automobile muffler or other heat source to store the heat. The stored heat can be used to dispel fog or sustain engine temperature. In other embodiments, the TES unit can be employed in any application which utilizes or require sustaining of thermal energy.

FIG. 8 shows an embodiment of a process 620 for storing and sustaining thermal energy. In one embodiment, a system with at least one TES unit stored in a tank is provided. For example, a plurality of TES units are stored in the tank. The TES units contain PCM having a threshold temperature T_(T). The threshold temperature, for example, can be the melting temperature of the PCM. A thermal transfer medium is circulated through the tank via input and output ports at step 655. The thermal transfer medium includes, for example, water or other type of fluid.

In one embodiment, the thermal transfer medium is imparted with thermal energy by an energy source. The energy source can be a renewable energy source such as solar energy. Alternatively, the energy source can be a combination of renewable and non-renewable energy. Non-renewable energy can additionally include thermal by-products of a non-renewable energy sources or processes. Circulating the thermal transfer medium through the system charges the TES units in the tank. Charging causes the PCM to change from a first phase to a second phase as thermal energy is stored. For heating applications, the temperature of the medium exceeds T_(T), causing the PCM to melt. As the PCM melts, thermal energy is stored. For cooling applications, the temperature of the medium is below T_(T), causing the PCM to solidify. As the PCM solidifies, thermal energy is stored.

At step 665, charging of the TES units is terminated. This happens, for example, in a situation where renewable energy is unavailable and/or the non-renewable energy source is switched off. The TES units, at step 675, are discharged. Discharging of the TES units releases thermal energy causing the PCM to change from the second phase to the first phase. The release of thermal energy sustains the thermal transfer medium at a temperature of, for example, about T_(T) for a prolonged period of time after termination of the energy source. The steps 655-675 can be repeated to continue the cyclical charging and discharging of the TES units to sustain the thermal medium at about T_(T).

The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of arrangements or a virtually any combination thereof.

The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected”, or “operably coupled”, to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable”, to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. 

1. A thermal storage (TES) unit comprising: a encasement with inner and outer surfaces; an internal cavity surrounded by the inner surface of the encasement; and at least a fin disposed in the cavity, the fin separate the cavity into a plurality of sub-cavities, the fin includes openings to provide communication between the sub-cavities; and a phase change material (PCM) to be disposed within the encasement, the PCM comprising a threshold temperature T_(T), a first temperature range corresponding to a first phase of the PCM and a second temperature range corresponding to a second phase of the PCM, wherein the fin increases thermal transfer efficiency of thermal energy between external environment of the TES unit and PCM.
 2. The unit of claim 1 comprising first and second halves coupled together to form the encasement.
 3. The unit of claim 2 wherein the external environment comprises a thermal transfer medium.
 4. The unit of claim 3 wherein the thermal transfer medium comprises water.
 5. The unit of claim 2 comprising an opening and a cap to facilitate filling of the encasement with PCM and sealing the encasement.
 6. The unit of claim 5 wherein the external environment comprises a thermal transfer medium.
 7. The unit of claim 6 wherein the thermal transfer medium comprises water.
 8. The unit of claim 1 wherein the external environment comprises a thermal transfer medium.
 9. The unit of claim 8 wherein the thermal transfer medium comprises water.
 10. The unit of claim 1 wherein T_(T) is a melting point of the PCM, wherein charging the TES unit comprises a charging temperature in a second temperature range to store thermal energy and discharging the TES unit comprises a discharge temperature in a first temperature range to dissipate thermal energy.
 11. The unit of claim 10 wherein the PCM comprises a PCM for storing thermal energy for heating applications.
 12. The unit of claim 11 wherein: the charging temperature in the second temperature range is greater than about T_(T); and the discharging temperature in the second temperature range is less than about T_(T).
 13. The unit of claim 10 wherein the PCM comprises a PCM for storing thermal energy for storing and sustaining heat to provide hot water.
 14. The unit of claim 10 wherein the PCM comprises a PCM for storing thermal energy for cooling applications.
 15. A method of storing thermal energy comprising: providing a TES unit including an encasement containing a PCM in an internal cavity of the encasement, the encasement includes at least a fin coupled to inner surface of the encasement to separate the cavity into a plurality of sub-cavities which are at least in fluid communication, the PCM comprising a threshold temperature T_(T), a first temperature range corresponding to a first phase of the PCM and a second temperature range corresponding to a second phase of the PCM; charging the TES unit with a thermal transfer medium at about a second temperature range to change the PCM from a first phase to a second phase, wherein the changing from the first phase to the second phase stores latent thermal energy; and discharging the TES unit at about a second temperature range to change the PCM from the second phase to the first phase to release latent thermal energy to sustain a thermal transfer medium temperature at about the threshold temperature.
 16. The method of claim 15 wherein the thermal transfer medium comprises water.
 17. The method of claim 16 wherein a plurality of TES units are provided in the tank.
 18. The method of claim 17 wherein the thermal energy stored provides thermal energy for heating.
 19. The method of claim 17 wherein the thermal energy stored provides thermal energy for cooling.
 20. A thermal energy storage system comprising: a tank with an input port and output port; at least one TES unit disposed in the tank, wherein a TES unit comprises an encasement with an internal cavity separated into sub-cavities which are in fluid communication by a fin partially coupled to an inner surface of the encasement; and an energy source coupled to the tank. 